1) Field of the Invention
The present invention relates to a mixing or stirring apparatus which reduces the vortex and increases the efficiency of the mixing process.
2) Description of Related Art
Many substances require mixing prior to use, such as paint. Paint is comprised of pigment, a vehicle or solvent, a binder and sometimes additives. These components tend to separate when the paint is stationary for some period and time and should be mixed prior to use. Mixing is also desired for other substances such as grout, mortar or other ingredients which do not naturally mix but need to be formed into an emulsion. Further, mixing to equilibrium is desired since it results in a mixing solution being less apt to separate into its original ingredients. Mixing of these sorts is desired in pharmaceuticals, paper, food preparation, cosmetics, and paint.
There have been many attempts to produce a suitable mixer for material such as paint, however, these attempts include undesirable aspects such as incomplete mixing, the undesirable creation of a vortex, and a very specific use of the mixer to achieve desirable results. For example, U.S. Pat. No. 2,879,044 discloses a paint mixing tool which includes a shank and a disk portion having spaced projections. This device includes inherent disadvantages. For example, when this device is improperly oriented in a container, a vortex is created (FIG. 7A) where the vortex 200 caused by the flow created by stirrer 204 results in particles 202 collecting at the bottom of the can, resulting in undesirable mixing. FIG. 7A shows the stirrer placed in an offset position and approximately 90° in relation to the surface of the substance to be mixed. In use, most individuals are unaware that this is the most undesirable orientation of a mixer in a container to achieve proper mixing, and specific knowledge about the mix is needed to effectively mix the substance. Further, the creation of a vortex places hydraulic stress on the shank and shortens the lifespan of the shaft and mixer.
One consequence of improperly using such a mixer is that when the user realizes that the pigment of paint is not mixing thoroughly, the user tends to increase the rotational speed of the mixer. This does not improve mixing, but rather requires more power and places greater stress on the shank. In one study, a 50% increase in rotational speed required 3 times more power to rotate the shank. However, the lack of a vortex indicates more efficient mixing and does not indicate that rotational speed should be increased. Determining proper mixing from viewing the surface of a substance to be mixed, such as paint which is opaque, can result in improper actions by the user which can lead to wasted energy without realization of mixing effectiveness.
Referring to FIG. 7B, the mixer is angled approximately 10° from vertical which results in a reduction of the vortex. Further, the mixer is placed approximately a distance of about ¼ to ⅓ diameter of the mixing container away from the edge of the container. However, this design, while an improvement, requires the specific orientation of the mixing shank to be 10° off center and placed ¼ to ⅓ of the length of the diameter of the mixing container form the side.
Further, the orientation of the mixer relative to the central axis 204 of the mixing container affects the effectiveness of the mixing. Optimally, the mixer is placed in a 15° offset to the central axis in the rotational direction 210 of the mixer as shown as 206 in FIG. 7C. This offset results in random collisions of the particles to be mixed and a more thorough mixing of the substance in the mixing chamber. When the mixer is parallel to the central axis of the mixing chamber as shown by 208, a vortex is created with all the disadvantages described above. When the mixer is placed in a 15° offset in the counter-rotational direction shown as 210, there is a swirling effect created in the substance to be mixed and the particles do not mix as uniformly. Therefore, there is a need for a mixing device that can be used with a rotary drive, such as a drill, which does not require such a specific orientation for maximizing effectiveness.
One attempt to overcome the disadvantages of the mixer creating a vortex is the use of tank baffles as illustrated in U.S. Pat. No. 4,150,900. The baffle can be located within the tank substantially at or just below the liquid surface. These baffles are spaced about the tank wall, and for a constant level agitated tank can be secured to the wall at a fixed location. It is suggested that a plurality of baffles should be used to increase the effectiveness of the agitator. However, the use of baffles increases the costs and risks damage to the mixer if the rotating mixer comes into contact with the baffles. This is particularly disadvantageous for paint mixing since paint is opaque and the physical location of the baffles generally cannot be seen by the user.
Another attempt to effectively mix materials such as paint is shown in U.S. Pat. No. 5,676,463 having a mixing paddle 212 (FIG. 7D) with a planar orientation. This design, when rotated, causes the flat surface 214 of the mixing blade to experience resistance as the surface area of the flat surface contacts the substance to be mixed (i.e., paint). Therefore, stress is placed on the mixing blade limiting the rotation speed and therefore the efficiency of the design. Further, when the paddle moves in a direction shown as 216, the movement of the flat surface of the mixing paddle through the paint creates a vacuum 218 on the trailing side 220 of the blade due to the flow of the paint 222 around the blade. This design does not efficiently mix paint at the rotational speed and therefore efficiency is limited by the design itself.
Further, these designs are prone to cause bubbles to form in the mixture, an undesirable results in paint, concrete and other substances that require mixing. There is a need for an efficient mixing apparatus which does not create bubbles or cause cavitations in the substance to be mixed.
Accordingly, it is an object of the present invention to provide an improved stirring apparatus that can be used to efficiently and effectively mix fluids and materials without creating a vortex in the substance to be mixed.
It is another object of the present invention to provide an improved stirring apparatus that can be operated without overly specific or complicated operating instructions.
It is another object of the present invention to provide an improved stirring apparatus that avoids shortening the operational life through improper use.